1. Field of the Invention
In many areas of electronic signal generation and signal processing, it is desirable to either make electronic signals of a particular wave shape, or to filter electronic signals to force them to acquire a given wave shape for a given input wave shape. The waveshaping of electronic signals is equivalent to attenuation and time displacement of various frequency bands of said signals. Of particular interest for many applications are the generation of pulses whose edges take on a sine squared shape, in order that the high frequency energy of these pulses is limited so as not to exceed a given frequency. The analysis of filters to perform such sine squared shaping has been investigated and reported: W. E. Thompson "The Synthesis of a Network to have a Sine Squared Impulse Response", Proc. IEE (London) Vol. 99, Part III p. 373, 1952; E. A. Guillemin "Synthesis of Passive Networks", New York, Wiley, 1957; and Arend Kastelein "A New Sine-Squared Pulse and Bar Shaping Network", IEEE Transactions on Broadcasting, Vol. BC-16, No. 4, Dec. 1970. Particular attention is given by the latter to shaping of synchronizing pusles for the television industry.
2. Description of the Prior Art
The shaping of electronic waveforms is generally accomplished by filters, both analog and digital, and in some applications, waveforms are generated by digital devices and converted to analog. Of these methods, the analog LC filter is the most common, requiring inductors and capacitors as circuit components. Generally for a reasonable level of performance for sine squared applications, 7-9 variable inductors and 7-9 capacitors, all having a tolerance in the 1 percent range, are required. These filters are fairly expensive and difficult to align properly, making their use somewhat limited, especially in lower cost equipment. For the television industry, and in particular the NTSC broadcast industry of the United States, it is generally accepted that the synchronizing pulses of video signals should have a sine squared shape with a 10% to 90% rise/fall time of 140 ns.+-.20 ns. This will ensure that all of the energy of the pulses is contained below the 4.2 Mhz bandwidth normally occupied by the video signal. The shaping of these synchronizing pulses is generally achieved by utilizing analog LC filters in more expensive equipment, or in lower cost equipment the pulses are given a trapezoidal shape to approximate a sine squared shape, but at a reduced level of conformity (and performance) to the generally accepted standard.